How to Find Hypersonic Stars Near the Milky Way's Biggest Black Hole

The center of our galaxy is a harsh, unforgiving place. A supermassive black hole cannibalizes entire stars, ejecting material millions of miles into space. The remaining gas is a thick soup of hydrogen and other elements so opaque that we can hardly see through it. And somewhere in that cloud of hydrogen and cosmic destruction, the supermassive black hole, Sagittarius A, batters around stars to incredible speeds.

It's been hard to measure all of what goes on inside the center, but radio astronomers think they have a solution to peering inside the cosmic maelstrom: they want to listen for something not unlike a stellar sonic boom. On Earth, a sonic boom occurs when an object travels faster than the speed of sound, building up air pressure into shock waves that make a loud crack.

In much the same way, hypervelocity stars traveling through cosmic dust would create shockwaves by going through the speed of "sound" in the dust. This involves speeds of thousands of miles per second, rather than 768 miles per hour as on Earth. These shockwaves could be detected by ground based radio telescopes, allowing a look into the mysterious cloud around the center of our galaxy.

In a paper to-be-published in the Monthly Notices of the Royal Astronomical Society (Arxiv pre-print available here), a Harvard-Smithsonian Center led team thinks they have the perfect test star. Known as S2, it's a star so bright it can be viewed through the dense cloud in infrared. It's also headed toward the center of the galaxy, making a close approach in 2017 or 2018. By listening for its "sonic booms," the team believes we could use it to calibrate radio telescope instruments for other similar events.

This would be a huge boon for astrophysicists, as it would put them one step closer to understanding the inner workings of the black holes at the center of every galaxy. It could also give us insight into what happens when you throw a star around at thousands of miles per second, which sounds ... intense.

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